Transmit diversity is one approach, which has been introduced in an attempt to increase downlink capacity within a network. Transmit diversity involves transmitting data on two or more antennas, sometimes referred to as an antenna array, which are spaced apart geographically. Generally, the signals transmitted from each antenna will have different path loss characteristics, which are largely independent of one another. When transmitted from multiple, spaced apart antennas, the signals from each of the antennas will interact with one another, generally resulting in a transmission pattern that includes some areas where the signals will constructively combine, and other areas where the signals will destructively interfere. In at least some instances, including instances involving a pair of spaced apart antennas, the pattern produced by the constructive and destructive areas will form lobes, which propagate outward from the area centered around the transmit antennas. However, the size and shape of the various areas is dependent upon the number and positioning of the spaced apart antennas, as well as the transmit characteristics of the signal being conveyed, such as phase and amplitude.
The particular areas in which the signals will constructively combine and destructively interfere can often be controlled by introducing phase adjustments, in one or more of the signal sources, relative to the other signal sources. In at least some instances, a phase adjustment will effectively involve a delay in the transmission of one signal relative to another. At least some of the value in controlling the areas in which the signals constructively combine and destructively interfere will allow a transmitted signal to be better received by an intended recipient located in an area where the composite signal levels are enhanced. Furthermore, the interfering affects of the transmitted signal for non-intended recipients located in an area where the signals do not readily coherently combine are reduced, as a result of a composite signal level that is generally diminished.
In addition to adjusting the phase of a signal, in at least some instances, the amplitude of one or more of the signals can also be adjusted, which in turn will further affect the transmission pattern. Generally transmission characteristics, such as phase and amplitude, relative to each of the signal sources, are referenced as weighting parameters, which in turn combine to produce a weighting pattern, that can be applied to an antenna array.
As a signal recipient moves relative to transmitted signal sources, in order to continue to enjoy the intended benefits of transmit diversity the weighting parameters applied to the two or more antennas occasionally may need to be updated to insure that the new area in which the intended signal recipient is located corresponds to an area in which the signal level of the composite signal is enhanced. In many instances, the new weighting parameters are determined at least in part by the intended recipient, in response to the most recently received signals. The weighting parameters are then communicated back to the entity managing the downlink communication through feedback as part of a corresponding uplink communication. The feedback can take the form of requested adjustments to the weighting parameters that are intended to maintain a more optimal performance level of the downlink signal, relative to the intended recipient.
However, when a communication link is initially established between an intended recipient and the entity managing the downlink communication and/or before the downlink managing entity has achieved synchronization with the intended recipient, the information being formulated and communicated as feedback can be problematic, as the intended recipient may be requesting updates to the weighting parameters, which may assume that previously requested adjustments, have already taken effect. For example, the intended recipient may by formulating further feedback in view of feedback which has been previously requested, but whose effects have not yet manifested in the communication channel. Consequently, the requested adjustments may be based on assumed communication conditions, which are not yet current relative to all of the previously requested adjustments. This can sometimes result in an incorrect adjustment, which may further complicate any attempted synchronization.
Still further the latency period prior to adopting previously requested feedback can be problematic in so far as it may result in the erroneous decoding of subsequently received information that continues to be transmitted in accordance with an earlier weighting value, where the intended recipient is attempting to decode the information in accordance with a requested adjustment, which has not yet been adopted. Any resulting erroneous decoding of communicated information will generally further complicate any future attempts to formulate further requested adjustments and any corresponding subsequent antenna weighting pattern.
Consequently, a method for synchronizing a wireless communication device and a wireless communication network having two or more antennas, which support transmit diversity, and a corresponding communication controller would be beneficial.